Hello all,
What went wrong in the following scenario? BTRFS thinks that a device is
mounted while it is not.
BTRFS tools ver: Btrfs v0.19-101-g3891d2d
Uname: 3.1.0-rc7-686-pae
## Comment: Initially we had only root (/) mounted as btrfs
mount |grep btrfs
/dev/sdc2 on / type btrfs (rw,autodefrag)
## Comment: Create a new btrfs fs on /dev/sdg /dev/sdh /dev/sdl
mkfs.btrfs -m raid1 -d raid1 /dev/sdg /dev/sdh /dev/sdl
btrfs filesystem show
Label: none uuid: f0425f63-e486-4c10-adab-47a23085c8db
Total devices 3 FS bytes used 28.00KB
devid 3 size 2.00GB used 200.00MB path /dev/sdl
devid 2 size 1.00GB used 200.00MB path /dev/sdh
devid 1 size 768.00MB used 404.00MB path /dev/sdg
Label: none uuid: cc8211ba-6f62-46d6-ba17-49250f06a941
Total devices 1 FS bytes used 512.98MB
devid 1 size 6.09GB used 1.75GB path /dev/sdc2
## Comment: unorthodox, but looks possible, add one of the devices from
the newly created fs to root (/)
btrfs device add /dev/sdh /
## Comment: Remove it back.
btrfs device delete /dev/sdh /
## Comment: We ended up with "*** Some devices missing" on both devices
btrfs filesystem show
Label: none uuid: 5910f378-0784-4e7f-b918-de35067252e9
Total devices 3 FS bytes used 28.00KB
devid 3 size 2.00GB used 200.00MB path /dev/sdl
devid 1 size 768.00MB used 404.00MB path /dev/sdg
*** Some devices missing
Label: none uuid: cc8211ba-6f62-46d6-ba17-49250f06a941
Total devices 2 FS bytes used 512.59MB
devid 1 size 6.09GB used 1.50GB path /dev/sdc2
*** Some devices missing
## Comment: Use btrfs balance to fix root (/)
btrfs filesystem balance /
btrfs filesystem show
Label: none uuid: 5910f378-0784-4e7f-b918-de35067252e9
Total devices 3 FS bytes used 28.00KB
devid 3 size 2.00GB used 200.00MB path /dev/sdl
devid 1 size 768.00MB used 404.00MB path /dev/sdg
*** Some devices missing
Label: none uuid: cc8211ba-6f62-46d6-ba17-49250f06a941
Total devices 1 FS bytes used 513.40MB
devid 1 size 6.09GB used 1.75GB path /dev/sdc2
## Comment: try to mount the initially created fs on /mnt. It fails
mount -t btrfs /dev/sdg /mnt
mount: wrong fs type, bad option, bad superblock on /dev/sdg,
missing codepage or helper program, or other error
In some cases useful info is found in syslog - try
dmesg | tail or so
## Comment: See if device scan can do the trick. Nope...
btrfs device scan /dev/sdh
Scanning for Btrfs filesystems in '/dev/sdh'
ERROR: unable to scan the device '/dev/sdh' - Invalid argument
## Comment: OK, we give up. Try to recreate btrfs from scratch
mkfs.btrfs -m raid1 -d raid1 /dev/sdg /dev/sdh /dev/sdl
WARNING! - Btrfs Btrfs v0.19 IS EXPERIMENTAL
WARNING! - see http://btrfs.wiki.kernel.org before using
/dev/sdh is mounted
## Comment: Of course /dev/sdh is not mounted.
mount |grep /dev/sdh
root@lxc:~#
Thanks,
Nikos
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